isl_coalesce.c: contains: improve error handling
isl_coalesce.c: contains: improve error handling

Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

inducer/isl-mirror,UBERTC/isl,PollyLabs/isl,nicolasvasilache/isl,Distrotech/isl,inducer/isl-mirror,KangDroidSMProject/ISL,PollyLabs/isl,Distrotech/isl,tobig/isl,BenzoSM/isl,simbuerg/isl,BenzoSM/isl,Distrotech/isl,nicolasvasilache/isl,BenzoSM/isl,nicolasvasilache/isl,abduld/isl,Meinersbur/isl,KangDroidSMProject/ISL,simbuerg/isl,UBERTC/isl,evaautomation/isl,UBERTC/isl,inducer/isl-mirror,tobig/isl,evaautomation/isl,BenzoSM/isl,Meinersbur/isl,tobig/isl,simbuerg/isl,nicolasvasilache/isl,abduld/isl,Distrotech/isl,simbuerg/isl,inducer/isl-mirror,KangDroidSMProject/ISL,KangDroidSMProject/ISL,abduld/isl,abduld/isl,PollyLabs/isl,BenzoSM/isl,nicolasvasilache/isl,simbuerg/isl,inducer/isl-mirror,KangDroidSMProject/ISL,PollyLabs/isl,evaautomation/isl,Meinersbur/isl,UBERTC/isl,PollyLabs/isl,evaautomation/isl,Distrotech/isl,tobig/isl,Meinersbur/isl